1. RHIZOBACTERIA AND THEIR APPLCATION
BAMGBOSE TIMOTHY
3rd SEM M.Sc
DOS in Microbiology
Manasagangotri
2. CONTENTS
INTRODUCTION
PLANT GROWTH PROMOTING RHIZOBACTERIA
APPLICATION
Rhizobacteria as Bioinoculant
Rhizobacteria as Biofertilizer
Rhizobacteria as Bioontrol
OTHER APPLICATION MECHANISM
Structural Mechanisms
Biochemical Mechanisms
Molecular Mechanisms
FUTURE PROSPECTS
3. INTRODUCTION
Rhizobacteria are root-
colonizing bacteria that form symbiotic
relationships with many plants(legumes
and Parasponia).
They are Gram-negative soil bacteria that fix
Nitrogen.
The name comes from the Greek rhiza, meaning root.
4. INTRODUCTION
The plant provides the bacteria
with organic compounds made
by photosynthesis.
Though parasitic varieties of
rhizobacteria exist, the term usually
refers to bacteria that form a
relationship beneficial for both parties
(mutualism).
5. PLANT GROWTH PROMOTING RHIZOBACTERIA
Rhizobacteria are often referred to as plant growth-
promoting rhizobacteria, or PGPRs.
First defined by Kloepper and Schroth to describe
soil bacteria that colonize the roots of plants
following inoculation onto seedand that
enhance plant growth.
PGPR enhance plant growth by direct and indirect
means, but the specific mechanisms involved have
not all been well-characterized
6.
7. APPLICATION
RHIZOBACTERIA AS BIOINOCULANT
Microbial inoculants also known as soil inoculants are agricultural
amendments that use beneficial endophytes (microbes) to promote
plant health.
Many of the microbes involved form symbiotic relationships with the
target crops where both parties benefit (mutualism).
Microbial inoculants are applied to improve plant nutrition, they can
also be used to promote plant growth by stimulating plant hormone
production.
Microbial inoculants can induce Systemic Acquired Resistance (SAR)
of crop species to several common crop diseases
8. APPLICATION
RHIZOBACTERIA AS BIOINOCULANT
Rhizobacterial Inoculants
The rhizobacteria commonly applied as inoculants includes nitrogen-fixers and
phosphate-solubilisers which enhance the availability of the macronutrients nitrogen
and phosphorus to the host plant.
Nitrogen-fixing bacteria
Rhizobium are Nitrogen-fixing bacteria that forms symbiotic associations within
nodules on the roots of legumes. This increases host nitrogen nutrition and is
important to the cultivation of soybeans, chickpeas and many other leguminous
crops.
For non-leguminous crops, Azospirillum has been demonstrated to be beneficial in
some cases for nitrogen fixation and plant nutrition.
For cereal crops, diazotrophic rhizobacteria have increased plant growth, grain yield,
nitrogen and phosphorus uptake, and nitrogen, phosphorus and potassium content.
9. APPLICATION
RHIZOBACTERIA AS BIOINOCULANT
Phosphate-solubilising bacteria
To improve phosphorus nutrition, the use of phosphate-solubilising
bacteria (PSB) such as Agrobacterium radiobacter has received attention.
PSB are free-living bacteria that break down inorganic soil phosphates to
simpler forms that enable uptake by plants.
Though microbial inoculants can be beneficial for crops, they are not
widely used in industrial agriculture, as large-scale application techniques
have yet to become economically viable. (exception is the use of rhizobial
inoculants for legumes such as peas.)
Inoculation with PGPR ensure efficient nitrogen fixation, and they have
been employed in North American agriculture for over 100 years.
10. APPLICATION
RHIZOBACTERIA AS BIOFERTILIZER
Bio-fertilizers add nutrients through the natural processes of:
Nitrogen fixation,
solubilizing phosphorus, and
stimulating plant growth through the synthesis of growth-
promoting substances.
Bio-fertilizers can be expected to reduce the use of chemical
fertilizers and pesticides .
Rhizobia can fix 40-120 kgs. of nitrogen per acre annually depending
upon the CROP, RHIZOBIUM SPECIES and ENVIRONMENTAL
CONDITIONS and have no negative effect on soil or the environment
Every leguminous crop requires a specific rhizobium species.
11. APPLICATION
RHIZOBACTERIA AS BIOFERTILIZER
A bio-fertilizer provides the following benefits:
• Readily and safely convert complex organic material in simple compounds,
so that plants are easily taken up.
• Improves soil fertility.
• It maintains the natural habitat of the soil.
• It increases crop yield by 20-30%, replaces chemical Nitrogen and
phosphorus by 25%, and stimulates plant growth.
• It can also provide protection against drought and some soil-borne
diseases.
• Bio-fertilizers are cost-effective relative to chemical fertilizers.
12. APPLICATION
RHIZOBACTERIA AS BIOCONTROL
Plant pathogens such as fungi, bacteria, viruses, nematodes etc. which
cause various diseases in crop plants are controlled by PGPR.
Mechanisms of biocontrol may be competition or antagonisms;
however, the most studied phenomenon is the induction of systemic
resistance by these rhizobacteria in the host plant.
PGPR control the damage to plants from pathogens by a number of
mechanisms including:
out-competing the pathogen by physical displacement,
secretion of siderophores to prevent pathogens in the
immediate vicinity from proliferating,
13. APPLICATION
RHIZOBACTERIA AS BIOCONTROL
Synthesis of antibiotics and variety of small molecules that
inhibit pathogen growth
Production of enzymes that inhibit the pathogen and
stimulation of the systemic resistance in the plants.
PGPR may also stimulate the production of biochemical
compounds associated with host defense.
Enhanced resistance may be due to:
Massive accumulation of phytoalexins, phenolic
compounds,
14. APPLICATION
RHIZOBACTERIA AS BIOCONTROL
defence enzymes and enhanced lignification
Biocontrol may also be improved by genetically
engineered PGPR to over express one or more of
these traits so that strains with several different anti-
pathogen traits can act synergistically.
Rhizobacteria-mediated Induced Systemic Resistant
(ISR) has been reported to be effective against fungi,
bacteria and viruses, but appears to involve different
signaling pathways and mechanisms.
15. OTHER APPLICATION MECHANISM
Structural Mechanisms
PGPR can induce structural changes in the host and
these changes were characterized by a considerable
enlargement of the callose-enriched wall appositions
deposited onto the inner surface of cell wall.
Pseudomonas fluorescens induced accumulation of
lignin in pea roots Bacillus pumilus SE34 showed a rapid
colonization of all tissues including the vascular stele in
tomato and induced resistance against Fusarium
oxysporum.
16. OTHER APPLICATION MECHANISM
Biochemical Mechanisms
PGPR are known to produce:
Antibiotics,
Antifungal metabolites,
Enzymes,
Phenolics,
Signal compounds and
other determinants of defence in response to pathogen
attack.
Various antibiotics like bacilysin, iturin-like lipopeptides,
diacetylphloroglucinol and pyrrolnitrin, HCN, phenazine-1-carboxylate
are produced by rhizobacteria
17. OTHER APPLICATION MECHANISM
Molecular Mechanisms
Mechanisms of rhizobacteria-mediated induced systemic resistance
(ISR) to the large extent are unknown. ISR in Arabidopsis mediated by
rhizobacteria is known not to be associated with a direct effect on
expression of known defence-related genes but stimulated the
expression of the jasmonate inducible gene Atvsp upon challenge.
ISR-expressing plants have the capacity to convert 1-
aminocyclopropane-1-carboxylate (ACC) to ethylene providing a
greater potential to produce ethylene upon pathogen attack.
Fluorescent pseudomonads are also known to produce salicylic acid,
which acts as local and systemic signal molecules in inducing
resistance in plants.
18. FUTURE PROSPECTS
Biocontrol has untapped potential and is underused,
underexploited, underestimated, often untried and therefore
unproven.
The new tools of recombinant DNA technology, mathematical
modeling, and computer technology combination with a
continuation of the more classical approaches such as importation
and release of natural enemies and improved germplasm,
breeding, and field testing should quickly move biocontrol
research and technology into a new era.
Biocontrol efficacy of PGPR may be improved by genetically
engineering them to over express one or more of these traits so
that strains with several different antiphytopathogen traits can act
synergistically.
19. CONCLUSION
PGPR mediated agriculture is now gaining worldwide
importance and acceptance for an increasing number of
crops and managed ecosystems as the safe method of
pest control AND bio-fertilizer.
For sustainable agricultural development and good eco-
environment establishment, a scientific fertilizer that
apply organic, inorganic and microbial fertilizers in a
balance and rational way to keep high and stable yield
will be good.
We can only move from here to getting better.
20. REFERENCES
Benizri, E., Baudoin, E., and Guckert, A. 2001. “Root colonization by inoculated plant growth
promoting rhizobacteria. Biocontrol” Sci. Technol. 11:557-574.
Glick, B. R. (1995).” The enhancement of plant growth by free-living bacteria”. Can. J.
Microbiol. 41:109-117.
Kloepper, J. W. (1993). “Plant growth-promoting rhizobacteria as biological control agents”.
Pages 255-274 in: Soil Microbial Ecology: Applications in Agricultural and Environmental
Management. F. B. Metting, Jr., ed. Marcel Dekker Inc., New York, USA.
Kloepper, J. W., and Schroth, M. N. (1978). “Plant growth-promoting rhizobacteria on
radishes”. Pages 879-882 in: Proc. of the 4th Internat. Conf. on Plant Pathogenic Bacter. Vol. 2,
Station de Pathologie Vegetale et Phytobacteriologie, INRA, Angers, France.
Niranjan Raj, S.,Shetty, H. S., M. S. Reddy ”Plant growth-promoting Rhizobacteria: Potential
green alternative for Plant productivity”
Vessy, J.K. (August 2003). "Plant Growth Promoting Rhizobacteria as Biofertilizers". Plant
and Soil 255: pp 571-586.
